My emails are not delivered or are filtered out as spam

Nowadays most mail servers have built-in antispam filters; they are quite smart, but sometimes they fail and delete (or mark as spam and redirect to some “spam” folder) perfectly legal messages; this is a common problem with Hotmail and other very popular free mail services. If you feel a lot of your messages are filtered out and not delivered, here are some basic rules to avoid being named a spammer by mistake: